Irrigation system with steady state speeds of movement

ABSTRACT

An irrigation system with steady state speeds of movement achieves and maintains substantial straight alignment of multiple interconnected spans with continuous movement over a range of speeds in a forward and reverse movement direction. A variable-speed drive controller monitors and processes the output of the corresponding alignment detector and, based on the output of the alignment detector, selects from memory and continuously furnishes to the corresponding span motor a predetermined progressively increasing speed profile, a predetermined progressively decreasing speed profile, or a new fixed current speed.

RELATED APPLICATIONS

The present application is a continuation of the Applicant's pendingU.S. patent application Ser. No. 14/599,718, filed on Jan. 19, 2015,entitled “An Irrigation System With Steady State Speeds Of Movement,”which was a continuation-in-part of U.S. patent application Ser. No.13/567,185, filed on Oct. 11, 2012, and now abandoned, which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to steady state speeds of movement forirrigation systems and more particularly pertains to a new system forachieving and maintaining substantial straight alignment of the spans ofan irrigation system with continuous movement over a range of speeds ina forward and reverse movement direction that minimizes or eliminatesstrenuous and repetitive start-and-stop movements by elements of theirrigation system.

Description of the Prior Art

Mechanized irrigation systems, such as center pivot or lateral moveirrigation systems, typically employ a series of pipe spans supportedabove a ground surface by tower structures that may include wheels orcrawler tracks mounted on the tower structures, that are driven toadvance the spans about a field in either a forward movement directionor a reverse movement direction. For the purposes of the presentinvention, the mechanized irrigation system will be referred to as theirrigation system and the pipes and the tower structures supporting thepipes will be referred to collectively as spans. Each of the spans moverelatively independently of the other spans, and the movement of thespans is often performed in a follow the leader type manner in which anend span initially advances in either a forward movement direction orreverse movement direction of the irrigation system, and the remainingintermediate spans follow thereafter.

The forward movement direction or reverse movement direction of theirrigation system is dependent on either a clockwise rotation or counterclockwise rotation of the central shafts of the rotors of the spanmotors connected to reduction gearboxes that drive the rotation of thewheels contacting the ground surface. The direction of the rotation ofthe central shafts of the rotors of the span motors are conventionallycontrolled by conductors supplying power, typically, 3-phase, 480 voltAC (alternating current), to the span motors. Conventional 3-phaseinduction motors provide inherently high starting torques and highefficiency in operation, typically at 60 Hz (cycles per second), onirrigation systems of the prior art and such motors may also be used asthe 3-phase span motors of the present invention.

In the case of 3-phase span motors as conventionally used on centerpivots, such span motors typically operate at a fixed span motor RPM(revolutions per minute) of approximately 1,750. Gear reduction isprovided to achieve a pace of movement over the ground of the wheels ofabout 0.8 wheel RPM. Such span motors can also easily be reversed (e.g.,clockwise rotation of the central shafts of the rotors of the spanmotors to counterclockwise rotation of the central shafts of the rotorsof the span motors). Reversal of the rotation of the central shafts ofthe rotors of the span motors is accomplished by simply reconfiguringthe connections of any two of the three conductors L1, L2, L3 of the3-phase supply power using a conventional electromechanical contactordevice, typically located at a central control panel (not shown). Thisfeature of 3-phase motors facilitates selecting a clockwise rotation orcounter clockwise rotation of the central shafts of the rotors of thespan motors, and, in turn, selecting either a forward movement directionor reverse movement direction of the irrigation system. A change ineither the forward movement direction or reverse movement direction ofthe irrigation system is controlled conventionally for both the priorart and for the system of the present invention by simply reconfiguringthe connections of any two of the three conductors L1, L2, L3 of the3-phase supply power.

Another convention of irrigation systems for the prior art is the usefixed-speed drive assemblies that may include an alignment detector withone or more single-pole, double-throw (SPDT) switches that are wired toreceive either a forward movement direction signal or a reverse movementdirection signal depending on either a forward movement direction or areverse movement direction. These typical SPDT switches control the spanmotors of the fixed-speed drive assembly on and off while the irrigationsystem is moving in either a forward movement direction or a reversemovement direction. The discrete forward and reverse movement directionsignals are communicated to the switches that each serve to signal twodistinct states of alignment to control the 3-phase span motors on andoff using a fixed-speed drive controller (e.g., electromechanicalcontactor or motor starter) of the fixed-speed drive assembly. Suchforward and reverse movement direction signals are typicallycommunicated to the switches using separately configured circuits ascompared to the three conductors L1, L2, L3 of the 3-phase supply powerthat are configured to supply electrical power to the span motors.

In an example of the prior art, a forward movement direction signal maybe present in a forward movement direction, and a reverse directionsignal may be present in a reverse movement direction. In operation,conventional center pivot controls include both a forward movementdirection signal and a reverse movement direction signal; however, onlyone of the two movement direction signals is present in a respectivemovement direction. Furthermore, the respective forward movementdirection signal and reverse movement direction signal are eachtypically configured to cause the switches to signal the fixed-speeddrive controller to control the span motors on and off in an oppositemanner with regard to maintaining span alignment. For example, with thesame state of alignment, a forward movement direction signal may beconfigured by the fixed-speed drive controller to control the span motoron and a reverse movement direction signal may be configured by thefixed-speed drive controller to control the span motor off.

The span motor of an intermediate span is typically controlled from spanmotor on to span motor off and span motor off to span motor on by afixed-speed drive controller that monitors the output of thecorresponding alignment detector that may include a single-pole,double-throw switch. Conventionally, in the prior art, the span motorRPM is not varied other than when the span motor is controlled from spanmotor on to span motor off and span motor off to span motor on. Suchswitch signals a discrete (i.e., binary logic, or two-state) on/offsignal switch state to cycle control the span motor in an on/off manner.The switch may be located at spans adjacent to the flexible junctureswhere adjacent spans are interconnected. Relative movement of adjacentspans actuates these switches and, for example, enables the signaling oftwo distinct states of alignment of adjacent interconnected spans, suchas that caused by the forward movement of an outer span about theflexible juncture of two adjacent spans. For example, the wheels of alagging intermediate tower structure are driven in a forward movementdirection by the rotation of one or more cams, rotated by one or morerods (e.g., mechanical linkage), that rotate against theroller-actuating arm of a corresponding switch that causes the internalcontacts of the respective switch to close in a conventionalsingle-pole, double-throw method that results in an “on” signal switchstate controlling the 3-phase span motor on. Furthermore, in thisexample, the supply power supplied to the span motor is configured torotate the central shaft of the rotor of such span motor in a clockwiserotation and, thereby, the span is driven in a forward movementdirection by a respective fixed-speed drive assembly until a substantialstraight alignment is restored between the adjacent spans (i.e.,respective intermediate tower structure not lagging and not leading).The switches signal two distinct states of alignment based on either aforward movement direction or a reverse movement direction and on aclosed switch contact or an opened switch contact that results in eithera span motor “on” control or a span motor “off” control.

The fixed-speed drive assemblies incorporating the span motors are,therefore, alternately and repeatedly controlled on and controlled offby way of a discrete “on” signal switch state or “off” signal switchstate. The wheels of the intermediate tower structures may each bedriven in either a forward movement direction or a reverse movementdirection at a uniform speed with closed switch contacts and stoppedwith opened switch contacts. This process is repeated by each successiveintermediate tower structure of the irrigation system until all of thespans are brought into substantial straight alignment. Each time anintermediate tower structure is advanced in either a forward movementdirection or a reverse movement direction, a new distinct state ofalignment is signaled by the corresponding switch and the process isrepeated.

In center pivot irrigation systems, the radially-outermost towerstructure or end tower structure typically leads the movement of thespans of the irrigation system, while in a lateral move irrigationsystem either one of the end tower structures typically leads themovement of the spans of the irrigation system. In a center pivotirrigation system, the outermost or end span wheel track has the largestcircumference; and, therefore, the end span has the farthest distance totravel. In the systems of the prior art the intermediate spans, havingrelatively smaller wheel track circumferences, can always keep up withthe speed of the end span while using substantially the same fixed-speedspan motors, assuming similar wheel tire sizes and gearing ratios.

This conventional manner of movement and substantial straight alignmentof the spans of irrigation systems requires countless starts-and-stopsby the intermediate tower structures, and the corresponding fixed-speeddrive assemblies that move them. The number of repeated on-and-offcontrol cycles of the corresponding span motor providing the movementfor a respective intermediate tower structure can exceed one thousand aday during continuous operation. This repeated on-and-off controlcycling of the corresponding span motors, which is repeated every day,all day, that the irrigation system is operating, causes excessive wearon the electrical components, structural components, and mechanicalparts of the fixed-speed drive assembly, especially the span motors,knuckles and gearboxes transferring power to the wheels.

To mitigate the stress on the irrigation system caused by the repetitivestart-and-stop movement of fixed-speed drive assemblies typicallyutilizing alignment detectors as discussed above, movement controlsystems have been proposed to provide a relatively smooth and continuousmovement of the intermediate spans and their respective intermediatetower structures. These continuous movement control systems typicallyemploy potentiometers or other analog sensors, such as capacitivedisplacement sensors, strain gauge sensors, non-contact proximitysensors or other devices capable of quantifiably measuring a precisedegree of span alignment. Analog alignment sensor signals vary inmagnitude in direct correlation or proportion to the degrees ofdeviation in alignment of one span with respect to adjacentinterconnected spans. Such analog alignment sensor signals are monitoredand processed by variable-speed drive controllers configured to varyaspects of the supply power (i.e., vary the speed) furnished to thecorresponding span motor. This, in turn, varies the span motor RPM that,in turn, varies the RPM of the wheels in response to changing analogalignment sensor signals. These analog type sensors are in lieu oftypical rod and switch actuators and cams or similar discrete signalingdevices that merely use a switch to signal if the state of alignment isbeyond a preset maximum value, as is the case with the conventionalsystems of the prior art for center pivot irrigation system movementcontrol systems.

The variations in the magnitude or intensity of analog sensor signalsare monitored and processed by variable-speed drive controllers that, inturn, vary aspects of the supply power (i.e., vary the speed) furnishedto the corresponding span motors turning the wheels of the intermediatetower structures in substantially direct correlation or proportion tothe degrees of deviation in alignment as detected and outputted by theanalog sensors, such that detection of greater angles of deviation inalignment of the interconnected spans results in relatively faster spanmotor speeds, and detection of relatively lower angles of deviation inalignment results in relatively slower span motor speeds. Such means ofvarying span motor speeds in direct proportion to the degrees ofdeviation in alignment as detected and outputted by the analog sensors(i.e., the selected speed of the variable-speed drive controller isbased upon the alignment) to maintain substantial straight alignment ofthe spans with continuous movement requires the span motors toconstantly transition between faster speeds and slower speeds (i.e.,transient state speeds of movement) as opposed to evolving to unchangingfixed-speeds (i.e., steady state speeds of movement).

Krieger (U.S. Pat. No. 6,755,362), Malsam (U.S. Patent App. Pub. No.2013/0018553) and Grabow (U.S. Patent App. Pub. No. 2013/0253752) haveproposed to provide a relatively smooth and continuous movement andsubstantial straight alignment of spans using potentiometers or otheranalog sensors or, in the case of Grabow, GPS (global positioningsystem) data is used as a means of generating analog alignment sensorsignals for varying span motor speeds in direct proportion to thedegrees of deviation in alignment.

SUMMARY OF THE INVENTION

The present invention discloses an irrigation system that is configuredto maintain substantial straight alignment of the spans of an irrigationsystem with continuous movement over a range of speeds in a forward andreverse movement direction. The present irrigation system includesmultiple interconnected spans that are supported by multiple towerstructures. Each intermediate tower structure may include avariable-speed drive assembly that may include a variable-speed drivecontroller that varies aspects of the supply power (i.e., varies thespeed) furnished to the corresponding span motor to control the speed ofmovement of the respective variable-speed drive assembly in either aforward movement direction or a reverse movement direction, suchvariable-speed drive controller selecting from memory and continuouslyfurnishing to the corresponding span motor a predetermined progressivelyincreasing speed profile, a predetermined progressively decreasing speedprofile, or a new fixed current speed so as to maintain span alignment.The predetermined progressively increasing speed profiles andpredetermined progressively decreasing speed profiles consist of one ormore rates of change in speed over time as opposed to a selected speed.The variable-speed drive assembly associated with each correspondingintermediate span includes an alignment detector configured to detectand output three distinct states of alignment. Such alignment detectormay include a conventional first switch one having two signal switch onestates, such as disclosed in the systems of the prior art, to provideeither an “on” signal switch one state or an “off” signal switch onestate and, in addition to the systems of the prior art, may include asecond switch two also having two signal switch two states to provideeither an “on” signal switch two state or an “off” signal switch twostate, but in an opposite manner to first switch one. For both switchone and switch two, the respective “on” signal switch states and the“off” signal switch states, monitored and processed by thevariable-speed drive controller, are based on four distinct states ofalignment (i.e., a lagging state of alignment, a non-lagging state ofalignment, a leading state of alignment, and a non-leading state ofalignment) of adjacent intermediate spans in either a forward movementdirection or a reverse movement direction.

In operation, the rotation of a cam against each respectiveroller-actuating arm one of switch one and roller-actuating arm two ofswitch two is configured in an opposite manner such that theroller-actuating arm one may cause the internal contacts of thecorresponding switch one to open and close in a conventional singlepole, double throw method, and, similarly, the roller-actuating arm twomay cause the internal contacts of the corresponding switch two to openand close in a conventional single pole, double throw method, but in anopposite manner to the internal contacts of switch one.

In an embodiment of the present invention, both switch one and switchtwo of the “dual switch” alignment detector may be conventional andtypical of the switch types used with electric-drive center pivotirrigation systems that utilize conventional span motors in conjunctionwith conventional, “single” switch, repetitive start-and-stop movementcontrol systems. For the conventional systems of the prior art, a“single switch” alignment detector with a single switch one is typicallyincorporated into each fixed-speed drive assembly of each intermediatetower structure and such conventional switch one is in communicationwith a respective fixed-speed drive controller configured to repeatedlyon-and-off control cycle the corresponding span motor to maintainsubstantial straight alignment of the spans of the irrigation system.

In the prior art, a switch one is typically incorporated into eachalignment detector of each fixed-speed drive assembly and is incommunication with a fixed-speed drive controller configured torepeatedly on-and-off control cycle the corresponding span motor tomaintain substantial straight alignment of the spans of the irrigationsystem with transient state speeds of movement (i.e., span motor on tospan motor off and span motor off to span motor on). In an embodiment ofthe present invention, the alignment detector of the variable-speeddrive assembly may utilize the same switch one, as described in theprior art, with an additional switch two, but wired in an oppositemanner, to communicate the “on” and “off” signal switch one states and“on” and “off” signal switch two states to a variable-speed drivecontroller. With the additional switch two having two signal switch twostates, the “dual switch” alignment detector is now capable of detectingat least three distinct states of alignment as opposed to prior artsystems only being capable of detecting two distinct states of alignmentas in the prior art. Both switch one and switch two of the alignmentdetector of the present invention may be conventional and typical of theswitch one type used with electric-drive center pivot irrigation systemsthat utilize span motors in conjunction with conventional repetitivestart-and-stop movement control systems.

In a preferred embodiment, the variable-speed drive controller of thepresent invention monitors and processes the output of the corresponding“dual switch” alignment detector and, based on the output of thealignment detector, selects from memory and continuously furnishes tothe corresponding span motor a predetermined progressively increasingspeed profile (e.g., in either a lagging state of alignment or anon-leading state of alignment), a predetermined progressivelydecreasing speed profile (e.g., in either a leading state of alignmentor a non-lagging state of alignment), or a new fixed current speed(e.g., in both a non-lagging state of alignment and a non-leading stateof alignment) (i.e., the selected predetermined progressively increasingspeed profiles, the selected predetermined progressively decreasingspeed profiles, and the selected new fixed current speeds of thevariable-speed drive controller are based upon the alignment). Inparticular, the variable-speed drive controller continuously furnishesto the corresponding span motor a predetermined progressively increasingspeed profile, a predetermined progressively decreasing speed profile,or a new fixed current speed. Thus, the variable-speed drive controllerprogressively increases the speed of the span motor in a predeterminedmanner over time, progressively decreases the speed of the span motor ina predetermined manner over time, or maintains a new fixed current speedof the span motor so as to maintain substantial straight alignment ofthe spans of the irrigation system with constantly evolving steady statespeeds of movement (i.e., the span motor evolves to a new fixed currentspan motor speed from the most current progressively increasing spanmotor speed and evolves to a new fixed current span motor speeds fromthe most current progressively decreasing span motor speed andeventually achieves a steady state of speed of movement that ultimatelymaintains both a non-lagging state of alignment and a non-leading stateof alignment for each respective span).

Prior art includes conventional repetitive start-and-stop movementcontrol systems, wherein “on” and “off” signal switch one states areoutputted by an alignment detector to a fixed-speed drive controllerthat, in turn, repeatedly on-and-off control cycles the correspondingspan motors. Significantly, the present invention may use an alignmentdetector with the same switch one to output the same “on” signal switchone states and “off” signal switch one states, but to a variable-speeddrive controller that, in addition, is also monitoring and processingthe output of additional “on” signal switch two states and “off” signalswitch two states of the same alignment detector. In other words, thepresent invention uses the same switch one to provide the same “on”signal switch one states and “off” signal switch one states to avariable-speed drive controller, but uses such “on” signal switch onestates and “off” signal switch one states in combination with a similarswitch two to provide additional “on” signal switch two states and “off”signal switch two states to be outputted by the alignment detector to acorresponding variable-speed drive controller for a total of four signalswitch states, two from each switch. The variable-speed drivecontroller, in turn, monitors and processes the output of thecorresponding alignment detector and, based on the output of thealignment detector, selects from memory and continuously furnishes tothe corresponding span motor a predetermined progressively increasingspeed profile, a predetermined progressively decreasing speed profile,or a new fixed current speed.

This, in turn, progressively increases the span motor speed in apredetermined manner over time, progressively decreases the span motorspeed in a predetermined manner over time, or maintains a new fixedcurrent speed of the span motor over time so as to maintain substantialstraight alignment of the spans of the irrigation system with constantlyevolving steady state speeds of movement. In contrast, the repetitivestart-and-stop movements of the prior art maintain substantial straightalignment of the spans of the irrigation system with transient statespeeds of movement while never evolving to preferred steady state speedsof movement.

A significant improvement in operation of irrigation systems by thesystem of the present invention as compared to the prior art is thesystem of enabling steady state speeds of movement rather than transientstate speeds of movement as required by conventional repetitivestart-and-stop movement control systems as well as all other continuousmovement control systems discussed herein. Furthermore, in the system ofthe present invention, the new fixed current speeds eventually evolve tosteady state speeds of movement of the variable-speed drive assembliesof each respective intermediate tower structure as the correspondingvariable-speed drive controller selects from memory and continuouslyfurnishes a predetermined progressively increasing speed profilefollowed by a new fixed current speed and a predetermined progressivelydecreasing speed profile followed by a new fixed current speed. Such newfixed current speeds eventually evolve to distinct steady state speedsof movement of the variable-speed drive assemblies of each respectiveintermediate tower structure that achieve and maintain alignment among aplurality of respective intermediate spans without the need forconstantly transitioning speeds or transient state speeds of movement aswith the repetitive start-and-stop movement control systems of the priorart as well all other continuous movement control systems.

It should be noted that both the conventional repetitive start-and-stopmovement control systems of the prior art and all other continuousmovement control systems serve to maintain substantial straightalignment of the spans of an irrigation system with transient statespeeds of movement. The present invention, however, further maintainsboth continuous movement and substantial straight alignment of the spansof an irrigation system with steady state speeds of movement over arange of speeds in a forward and reverse movement direction withouttransient state speeds of movement or the strenuous and repetitivestart-and-stop movements of the prior art that result from repeatedon-and-off control cycling of the corresponding span motors.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures:

FIG. 1A is an isometric diagrammatic perspective view of an irrigationsystem in accordance with an example implementation of the prior art.

FIG. 1B is an isometric diagrammatic perspective view of an irrigationsystem in accordance with an example implementation of the presentinvention.

FIG. 2A is a schematic diagram illustrating the selected elements of thefixed-speed drive assembly of the irrigation system shown in FIG. 1A inaccordance with an example implementation of the prior art.

FIG. 2B is a schematic diagram illustrating the selected elements of thevariable-speed drive assembly of the irrigation system shown in FIG. 1Bin accordance with an example implementation of the present invention.

FIG. 3A is a block diagram illustrating the selected elements of thefixed-speed drive assembly of the irrigation system shown in FIG. 1A inaccordance with an example implementation of the prior art.

FIG. 3B is a block diagram illustrating the selected elements of thevariable-speed drive assembly of the irrigation system shown in FIG. 1Bin accordance with an example implementation of the present invention.

FIG. 3C is a block diagram illustrating the selected elements of thevariable-speed drive controller of the irrigation system shown in FIG.1B in accordance with an example implementation of the presentinvention.

FIG. 3D is a block diagram illustrating the selected elements of thevariable-speed drive assembly of the irrigation system shown in FIG. 1Bin accordance with an example implementation of the present invention.

FIG. 3E is a block diagram illustrating the selected elements of thevariable-speed drive assembly of the irrigation system shown in FIG. 1Bin accordance with an example implementation of the present invention.

FIG. 3F is a block diagram illustrating the selected elements of thevariable-speed drive assembly of the irrigation system shown in FIG. 1Bin accordance with an example implementation of the present invention.

FIG. 4A is an illustration of the respective longitudinal axes of thespans of an irrigation system shown in FIGS. 1A and 1B in substantialstraight alignment in either a forward movement direction or a reversemovement direction in accordance with an example implementation of theprior art and with an example implementation of the present invention.

FIG. 4B is an illustration of the respective longitudinal axes of thespans of an irrigation system shown in FIGS. 1A and 1B in deviations inalignment in a forward movement direction in accordance with an exampleimplementation of the prior art and with an example implementation ofthe present invention.

FIG. 4C is an illustration of the respective longitudinal axes of thespans of an irrigation system shown in FIGS. 1A and 1B in deviations inalignment in a reverse movement direction in accordance with an exampleimplementation of the prior art and with an example implementation ofthe present invention.

FIG. 5A is a schematic diagram illustrating the selected elements ofswitch one shown in FIGS. 2A and 2B in a forward movement direction inaccordance with an example implementation of the prior art and with anexample implementation of the present invention.

FIG. 5B is a schematic diagram illustrating the selected elements of theswitch one shown in FIGS. 2A and 2B in a reverse movement direction inaccordance with an example implementation of the prior art and with anexample implementation of the present invention.

FIG. 5C is a schematic diagram illustrating the selected elements ofswitch two shown in FIG. 2B in a forward movement direction inaccordance with an example implementation of the present invention.

FIG. 5D is a schematic diagram illustrating the selected elements ofswitch two shown in FIG. 2B in a reverse movement direction inaccordance with an example implementation of the present invention.

FIG. 6A is a graphical diagram illustrating the signal magnitudes ofswitch one of the irrigation system shown in FIGS. 1A and 1B inaccordance with an example implementation of the prior art and with anexample implementation of the present invention.

FIG. 6B is a graphical diagram illustrating the signal magnitudes ofswitch two of the irrigation system shown in FIG. 1B in accordance withan example implementation of the present invention.

FIG. 7 is a graphical diagram illustrating a predetermined progressivelyincreasing speed profile, a predetermined progressively decreasing speedprofile, and a new fixed current speed of the variable-speed drivecontroller, such speed profiles and new fixed current speeds selectedfrom memory and continuously furnished to the span motors of theirrigation system shown in FIG. 1B in accordance with an exampleimplementation of the present invention.

FIG. 8A is a graphical diagram illustrating transient state speeds ofmovement that result from the fixed-speed drive controller of theirrigation system shown in FIG. 1A in accordance with an example of theprior art repeatedly control cycling between span motor on and spanmotor off.

FIG. 8B is a graphical diagram illustrating steady state speeds ofmovement that evolve from alternating predetermined progressivelyincreasing speed profiles, predetermined progressively decreasing speedprofiles, and new fixed current speeds of the variable-speed drivecontroller selected from memory and continuously furnished to thecorresponding span motors of the irrigation system shown in FIG. 1B inaccordance with an example implementation of the present invention.

FIG. 9A is a block diagram illustrating the first of two switch oneconfigurations of the present invention of the irrigation system shownin FIG. 1B in accordance with an example implementation of the presentinvention.

FIG. 9B is a block diagram illustrating the first of two switch twoconfigurations of the present invention of the irrigation system shownin FIG. 1B in accordance with an example implementation of the presentinvention.

FIG. 9C is a block diagram illustrating the second of two switch oneconfigurations of the present invention of the irrigation system shownin FIG. 1B in accordance with an example implementation of the presentinvention.

FIG. 9D is a block diagram illustrating the second of two switch twoconfigurations of the present invention of the irrigation system shownin FIG. 1B in accordance with an example implementation of the presentinvention.

FIG. 10A is a block diagram illustrating the first of two switch one andswitch two configurations and the first configuration of sixteen totalconfigurations of the present invention of the irrigation system shownin FIG. 1B in accordance with an example implementation of the presentinvention.

FIG. 10B is a block diagram illustrating the second of two switch oneand switch two configurations and the first configuration of sixteentotal configurations of the present invention of the irrigation systemshown in FIG. 1B in accordance with an example implementation of thepresent invention.

FIG. 10C is a block diagram illustrating the first of two switch one andswitch two configurations and the second configuration of sixteen totalconfigurations of the present invention of the irrigation system shownin FIG. 1B in accordance with an example implementation of the presentinvention.

FIG. 10D is a block diagram illustrating the second of two switch oneand switch two configurations and the second configuration of sixteentotal configurations of the present invention of the irrigation systemshown in FIG. 1B in accordance with an example implementation of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Overview.

Irrigation systems, such as center pivot irrigation systems, generallyinclude fixed-speed drive assemblies at each of the intermediate towerstructures to propel the irrigation systems over a respective groundsurface, cultivation area or field. Such irrigation systems rely on spanmotors with fixed-rate speeds of the central shafts of the rotors ofsuch span motors due to their relative simplicity and robustness. Suchsystems, however, can only adjust the relative alignment of various spanportions by repeatedly on-and-off control cycling the corresponding spanmotors as roving spans change states of alignment in either a forwardmovement direction or a reverse movement direction. This results in eachintermediate tower structure coming to a complete stop and thenrequiring a large impulse of power to the span motor to start theintermediate tower structure moving again. These strenuous andrepetitive start-and-stop movements that result from repeated on-and-offcontrol cycling of the corresponding span motors can result in excessivestress on structures, wear on components, and downtime of the irrigationsystem. The irregular motion caused by these strenuous and repetitivestart-and-stop movements in order to maintain a substantial straightalignment of the spans can also cause uneven application of irrigationwater and/or chemicals to the field. This results in waste of both waterand chemicals. The irregular motion can also cause deviations inalignment or errors in determining the position of the end of themachine. This can result in errors in operations based on position.

Accordingly, an irrigation system with steady state speeds of movementis disclosed that is configured to maintain a substantial straightalignment among multiple adjacent spans without the irregular motioncaused by the strenuous and repetitive start-and-stop movements whereinspan motors are repeatedly control cycled between span motor on and spanmotor off as described above. In an implementation, an irrigation systemincludes multiple interconnected spans that are supported by multipletower structures. Each intermediate tower structure may include avariable-speed drive that may include a variable-speed drive controllerthat varies aspects of the supply power (i.e., varies the speed)furnished to the corresponding span motor to control the speed ofmovement of the respective variable-speed drive assembly in either aforward movement direction or a reverse movement direction, suchvariable-speed drive controller selecting from memory and continuouslyfurnishing to the corresponding span motor a predetermined progressivelyincreasing speed profile or a predetermined progressively decreasingspeed profile so as to maintain span alignment. Such predetermined speedprofiles may consist of one or more rates of change in speed over time(e.g., ramp up speed, ramp down speed, step up speed, step down speed,etc.).

In an embodiment of the present invention, each variable-speed driveassembly of the intermediate spans of the irrigation system may includean alignment detector configured to detect and output three distinctstates of alignment. Such alignment detector may include a switch onehaving two signal switch one states with a roller-actuating arm one anda switch two having two signal switch two states with a roller-actuatingarm two that are each actuated by the rotational movement of a camconnected to a rod associated with a corresponding intermediate span tosignal four distinct states of alignment of the corresponding span withrespect to an adjacent span. Within each variable-speed drive assembly,an alignment detector with a corresponding switch one and acorresponding switch two is in communication with a correspondingvariable-speed drive controller. Each variable-speed drive controller isconfigured to monitor and process the output of the correspondingalignment detector and, based on the output of the alignment detector,to select from memory and continuously furnish to the corresponding spanmotor a predetermined progressively increasing speed profile, apredetermined progressively decreasing speed profile, or a new fixedcurrent speed so as to maintain the interconnected spans in asubstantially linear orientation to the respective longitudinal axes ofthe spans (e.g., maintain substantial straight alignment of the spanswith respect to each other).

Similarly, such new fixed current speeds may be equal to the speedcurrently being furnished by the variable-speed drive controller to thecorresponding span motor at the exact moment when a predeterminedprogressively increasing speed profile or a predetermined progressivelydecreasing speed profile changes to a new fixed current speed.

As disclosed by the present invention, the variable-speed drivecontroller selects from memory and continuously furnishes to thecorresponding span motor a new fixed current speed each time apredetermined progressively increasing speed profile or a predeterminedprogressively decreasing speed profile causes a change in the state ofalignment, as detected and outputted by the alignment detector, betweentwo adjacent spans. In reaction to span movements resulting from thevariable-speed drive controller selecting from memory and continuouslyfurnishing to the corresponding span motor predetermined progressivelyincreasing speed profiles followed by a new fixed current speed andpredetermined progressively decreasing speed profiles followed by a newfixed current speed, the rotation of one or more cams, rotated by one ormore rods, actuates either or both the roller-actuating arm one ofswitch one and the roller-actuating arm two of switch two. Thevariable-speed drive controller monitors and processes the output of thecorresponding alignment detector (i.e., signal switch one states andsignal switch two states).

A significant and unique improvement in operation of irrigation systemsby the system of the present invention as compared to the repetitivestart-and-stop movement control systems of the prior art as well as allother continuous movement control systems, is the evolving of steadystate speeds of movement rather than constantly transitioning ortransient state speeds of movement from span motor on to span motor offand span motor off to span motor on, as required by the repetitivestart-and-stop movement control system of the prior art, or from slowerspan motor speeds to faster span motor speeds and faster span motorspeeds to slower span motor speeds, as required by all other continuousmovement control systems discussed herein. In the system of the presentinvention, the new fixed current speeds eventually evolve to steadystate speeds of movement of the variable-speed drive assemblies of eachrespective intermediate tower structure as the correspondingvariable-speed drive controller selects from memory and continuouslyfurnishes to the corresponding span motor a predetermined progressivelyincreasing speed profile followed by a new fixed current speed and apredetermined progressively decreasing speed profile followed by a newfixed current speed. Such new fixed current speeds eventually evolve todistinct steady state speeds of movement of the variable-speed driveassemblies of each respective intermediate tower structure that achieveand maintain alignment among a plurality of respective intermediatespans without the need for constantly transitioning speeds or transientstate speeds of movement as with the repetitive start-and-stop movementcontrol systems of the prior art as well all other continuous movementcontrol systems.

In an embodiment, each variable-speed drive assembly of the irrigationsystem may include a switch one and a switch two that may each besimultaneously and individually actuated by the rotational movement ofone or more cams against a respective roller-actuating arm one of switchone and a respective roller-actuating arm two of switch two to signaldistinct states of alignment of the corresponding span with respect toan adjacent span. Within each variable-speed drive assembly, such switchone and switch two of a respective alignment detector may each be incommunication with a corresponding variable-speed drive controller. Eachvariable-speed drive controller may be configured to monitor and process“on” signal switch one state, “off” signal switch one state, “on” signalswitch two state, and “off” signal switch two state data and use suchprocessed “on” signal switch one state, “off” signal switch one state,“on” signal switch two state, and “off” signal switch two state data toselect from memory and continuously furnish to the corresponding spanmotor a predetermined progressively increasing speed profile, apredetermined progressively decreasing speed profile, or a new fixedcurrent speed so as to maintain the interconnected spans in asubstantially linear orientation to the respective longitudinal axes ofthe spans (e.g., maintain substantial straight alignment of the spanswith respect to each other).

Prior Art.

FIG. 1A illustrates a self-propelled (e.g., mechanized) irrigationsystem 1 in accordance with an embodiment of the prior art. Examples ofself-propelled irrigation systems include a center pivot irrigationsystem 1, a linear move irrigation system (not shown), or the like. FIG.1A illustrates an embodiment of the prior art wherein the irrigationsystem 1 is a center pivot irrigation system. As shown, the irrigationsystem 1 may include a center pivot point structure 2, a main sectionassembly 10 (irrigation section assembly) coupled (e.g., connected) tothe center pivot point structure 2. The center pivot point structure 2has access to a water source to furnish water to the irrigation system1.

FIG. 2A illustrates a fixed-speed drive assembly 34 typical ofconventional irrigation systems 1. Each fixed-speed drive assembly 34may include an alignment detector 48 (including a switch one 40 with aroller-actuating arm one 88, a normally closed switch one contact 80, anormally opened switch one contact 81, and a common switch one contact82, a cam 83, and a rod 87), a span motor 38, wheels 36, and afixed-speed drive controller 37. The fixed-speed drive controller 37typically used in the prior art is an electromechanical contactor ormotor starter that controls the repeated on-and-off control cycling ofeach corresponding span motor 38, such repeated on-and-off controlcycling of each corresponding span motor 38 being necessary to achieveand maintain substantial straight alignment of the spans and speed ofmovement in either a forward movement direction 54 or a reverse movementdirection 55 while the irrigation system 1 is operating.

FIG. 3A is a block diagram illustrating selected elements of thefixed-speed drive assembly 34 of the irrigation system 1 shown in FIG.1A in accordance with an example implementation of the prior art.

FIGS. 4A, 4B, and 4C are illustrations of the respective longitudinalaxes of the intermediate spans 12, 13 and end span 14 with deviations inalignment in either a forward movement direction 54 or a reversemovement direction 55 of an irrigation system 1 shown in FIG. 1A inaccordance with an example implementation of the prior art.

FIG. 5A is two schematic diagrams of switch one 40 of the irrigationsystem 1 shown in FIG. 1A in a forward movement direction 54illustrating the double pole, single throw method of a switch one 40configured in the upper diagram to indicate switch one 40 in an onsignal switch one state 66 and in the lower diagram to indicate switchone 40 in an off signal switch one state 62 in accordance with anexample implementation of the prior art.

FIG. 5B is two schematic diagrams of switch one 40 of the irrigationsystem 1 shown in FIG. 1A in a reverse movement direction 55illustrating the double pole, single throw method of switch one 40configured in the upper diagram to indicate switch one 40 in an offsignal switch one state 62 and in the lower diagram to indicate switchone 40 in an on signal switch one state 66 in accordance with an exampleimplementation of the prior art.

FIG. 6A is a graphical diagram illustrating the signal magnitudes ofswitch one 40 of the irrigation system 1 shown in FIG. 1A in accordancewith an example implementation of the prior art.

FIG. 8A is a graphical diagram illustrating transient state speeds ofmovement 79 that result from the fixed-speed drive controller 37 of theirrigation system 1 shown in FIG. 1A in accordance with an example ofthe prior art repeatedly control cycling between span motor on 60 andspan motor off 61. The fixed-speed drive controller 37 controls the spanmotor on 60 based on an “on” signal switch status 66 and controls thespan motor off 61 based on an “off” signal switch status 62.

Example Implementations of the Present Invention.

FIG. 1B illustrates a self-propelled (e.g., mechanized) irrigationsystem (assembly) 1 in accordance with example implementations of thepresent invention. Examples of self-propelled irrigation systems includea center pivot irrigation system, a linear move irrigation system, orthe like. FIG. 1B illustrates an embodiment of the present inventionwherein the irrigation system 1 is a center pivot irrigation system.However, it is contemplated that the present invention may beimplemented in other self-propelled irrigation systems (e.g., linearmove irrigation systems). As shown, the irrigation system 1 may includea center pivot point structure 2, a main section assembly 10 (irrigationsection assembly) coupled (e.g., connected) to the center pivot pointstructure 2. The center pivot point structure 2 has access to a watersource to furnish water to the irrigation system 1.

The main section assembly 10 includes a number of interconnectedintermediate spans 12, 13 with applicant conduits 24, 25 that are eachsupported by a truss-type framework structure 6, 7 and by one or moreintermediate tower structures 30, 31 and an interconnected end span 14with applicant conduit 26 that is supported by a truss-type frameworkstructure 8 and by an end tower structure 32. The intermediate towerstructures 30, 31 and end tower structure 32 may be any towerconfiguration known in the art to adequately support the applicantconduits 24, 25, 26, (e.g., pipes) described herein. It is to beunderstood that the main section assembly 10 may include any number ofspans 24, 25, 26 and intermediate tower structures 30, 31 and end towerstructure 32. The direction of travel for the main section assembly 10can be either a forward movement direction 54 or a reverse movementdirection 55. The intermediate tower structures 30, 31 and the end towerstructure 32 each may include one or more wheels 36, to assist intraversing the irrigation system 1 so as to pivot the main sectionassembly 10 about a ground surface, cultivation area or field in aforward movement direction 54 or a reverse movement direction 55 alongwheel tracks 50, 51, 52. As shown in FIGS. 1A and 1B, each intermediatespan 12, 13 and the end span 14 may include applicant conduits 24, 25,26 (e.g., pipes) that are configured to carry liquid (e.g., applicant)along the length of the irrigation system 1 to one or more applicantdispersal assemblies that are configured to irrigate the cultivationarea. Each conduit 24, 25, 26 may be coupled to one another to allowfluid communication between each conduit. In an implementation, theapplicant conduits 24, 25, 26 may be supported by truss-type frameworkstructures 6, 7, 8. Thus, the main fluid displacement device may beconfigured to displace applicant through the applicant conduits 24, 25,26. As shown in FIGS. 1A and 1B, the irrigation system 1 also mayinclude a cantilevered boom structure 5 that extends outwardly from theend tower structure 32.

Both the forward movement direction 54 and the reverse movementdirection 55 are dependent on the direction of rotation of the centralshafts of the rotors of the span motors 38. The wiring configuration of3-phase supply power 67 conductor-L1 68, conductor-L2 69 andconductor-L3 70 (FIGS. 2A and 2B) included in incoming span cable 20 andoutgoing span cable 21 may be configured to result in either a clockwiserotation or a counter clockwise rotation of the central shafts of therotors of the span motors 38. Simply reconfiguring two of the three3-phase supply power 67 conductor-L1 68, conductor-L2 69 andconductor-L3 70 results in a reversal of the rotation of the centralshafts of the rotors of the span motors 38. Thus, in operation, theforward movement direction 54 or reverse movement direction 55 forirrigation system 1 is conventionally changed, both in the prior art andin the system of the present invention, from forward to reverse orreverse to forward using an electromechanical contactor device,typically located at a central control panel (not shown) and controlledby an operator, connected to span cable out 20 at a central controlpanel (not shown) at center pivot point structure 2 (FIGS. 1A and 1B).The operation of said electromechanical contactor device configures3-phase supply power 67 conductor-L1 68, conductor-L2 69 andconductor-L3 70 (FIGS. 2A and 2B) in incoming span cable 20 so as toprovide either a clockwise rotation or a counter clockwise rotation ofthe central shafts of the rotors of the span motors 38 that results inthe desired forward movement direction 54 or reverse movement direction55, as selected by an operator.

With reference to FIGS. 2A and 2B, it should also be noted thattypically the same electromechanical contactor device, typically locatedat a central control panel (not shown) and controlled by an operator,that configures 3-phase supply power 67 conductor-L1 68, conductor-L2 69and conductor-L3 70 to set the rotation of the central shafts of therotors of span motors 38 to result in either a forward movementdirection 54 or a reverse movement direction 55 also provides therespective forward direction signal 22 or reverse direction signal 23.

With reference to FIG. 2B, each variable-speed drive assembly 35 mayinclude an alignment detector 48 (including a switch one 40 with aroller-actuating arm one 88, a normally closed switch one contact 80, anormally opened switch one contact 81, and a common switch one contact82, and including a switch two 41 with a roller-actuating arm two 89, anormally closed switch two contact 84, a normally opened switch twocontact 85, and a common switch two contact 86, a cam 83, and a rod 87),a span motor 38, wheels 36, and a variable-speed drive controller 39that varies aspects of the supply power 67 (i.e., varies the speed)furnished to the corresponding span motor 38. The forward directionsignal 22 and reverse direction signal 23 are communicated to thevariable-speed drive assembly 35 by way of incoming span cable 20 andoutgoing span cable 21. The forward direction signal 22 and reversedirection signal 23 are each discretely connected by wire or other meansto switch one 40 and, in an opposite manner, to switch two 41 ofalignment detector 48 in the variable-speed drive assembly 35.Furthermore and with reference to the alignment detector 48 shown inFIG. 2B, the rotation of cam 83, rotated by one or more rods 87, mayactuate roller-actuating arm one 88 of switch one 40 in an oppositemanner as compared to roller-actuating arm two 89 of switch two 41.

With reference to FIGS. 2B, 5A and 5B, the forward direction signal 22circuit is conventionally connected to a normally closed switch onecontact 80 in switch one 40 and the reverse direction signal 23 circuitis conventionally connected to a normally opened switch one contact 81in switch one 40 (although in an embodiment this configuration could bedifferent). The actuation of roller-actuating arm one 88 of switch one40 by the rotation of one or more cams 83, rotated by one or more rods87, connects the common switch one contact 82 of switch one 40alternatively either to the normally closed switch one contact 80 (e.g.,to the forward direction signal 22), or to the normally opened switchone contact 81 (e.g., to the reverse direction signal 23). The forwarddirection signal 22 and reverse direction signal 23 as determined by theforward movement direction 54 and reverse movement direction 55 isthereby either closed to the common switch one contact 82 of switch one40 or opened to the common switch one contact 82 of switch one 40, asdetermined by the position of roller-actuating arm one 88 against cam83. Thereby, common switch one contact 82 signals either an “off” signalswitch one state 62 or an “on” signal switch one state 66 tovariable-speed drive controller 39 based, first, on either a forwarddirection signal 22 or a reverse direction signal 23 and, second, on theconnection of common switch one contact 82 to either the normally closedswitch one contact 80 or the normally opened switch one contact 81. Thecommon switch one contact 82 is (i.e., signals an “on” signal switch onestate 66) when either a forward direction signal 22 or reverse directionsignal 23 is enabled to pass through switch one 40 based on the positionof roller-actuating arm one 88 against cam 83, rotated by one or morecorresponding rods 87. The common switch one contact 82 is de-energized(i.e., signals an “off” signal switch one state 62) when neither aforward direction signal 22 nor reverse direction signal 23 is enabledto pass through switch one 40 based on the position of the correspondingcam 83, rotated by one or more corresponding rods 87. In operation,alignment detector 48 outputs either an “on” signal switch one state 66or an “off” signal switch one state 62, such output of alignmentdetector 48 being monitored and processed by the variable-speed drivecontroller 39 as shown in FIGS. 2B, 5A, 5B, 9A and 9C.

Additionally and with reference to FIGS. 2B, 5C and 5D, the forwarddirection signal 22 circuit is connected to a normally opened switch twocontact 85 in switch two 41 and the reverse direction signal 23 circuitis connected to a normally closed switch two contact 84 in switch two 41(although in an embodiment this configuration could be different). Theactuation of roller-actuating arm two 89 of switch two 41 by therotation of one or more cams 83, rotated by one or more rods 87,connects the common switch two contact 86 of switch two 41 alternativelyeither to the normally closed switch two contact 84 (e.g., to thereverse direction signal 23), or to the normally opened switch twocontact 85 (e.g., to the forward direction signal 22). The forwarddirection signal 22 and reverse direction signal 23 as determined by theforward movement direction 54 and reverse movement direction 55 arethereby either closed to the common switch two contact 86 of switch two41 or opened to the common switch two contact 86 of switch two 41, asdetermined by the position of cam 83, rotated by one or more rods 87,and resulting actuation of roller-actuating arm two 89 of switch two 41.Thereby, common switch two contact 86 signals either an “off” signalswitch two state 63 or an “on” signal switch two state 65 tovariable-speed drive controller 39 based, first, on either a forwarddirection signal 22 or a reverse direction signal 23 and, second, on theconnection of common switch two contact 86 to either the normally closedswitch two contact 84 or the normally opened switch two contact 85. Thecommon switch two contact 86 is energized (i.e., signals an “on” signalswitch two state 65) when either a forward direction signal 22 orreverse direction signal 23 is enabled to pass through switch two 41based on the position of roller-actuating arm two 89 against cam 83,rotated by one or more corresponding rods 87. The common switch twocontact 86 is de-energized (i.e., signals an “off” signal switch twostate 63) when neither a forward direction signal 22 nor reversedirection signal 23 is enabled to pass through switch two 41 based onthe position of the corresponding cam 83, rotated by one or morecorresponding rods 87. In operation, alignment detector 48 outputseither an “on” signal switch two state 65 or an “off” signal switch twostate 63, such output of alignment detector 48 being monitored andprocessed by the variable-speed drive controller 39 as shown in FIGS.2B, 5C, 5B, 9B and 9D.

Simultaneously and in combination, alignment detector 48 outputs to theprocessor 42 (shown in FIG. 3C) of variable-speed drive controller 39either an “on” signal switch one state 66 or an “off” signal switch onestate 62 (FIGS. 2B, 5A, 5B, 9A and 9C) and either an “on” signal switchtwo state 65 or an “off” signal switch two state 63 (FIGS. 2B, 5C, 5D,9B and 9D).

Furthermore, in a preferred embodiment, the processor 42 ofvariable-speed drive controller 39 (shown in FIGS. 10A and 10B)processes the following two signal switch one states 62, 66 and signalswitch two states 63, 65 combinations:

signal signal switch one switch two 66 + 65 (not shown in FIG. 2B) 62 +63 (not shown in FIG. 2B) 66 + 63 (as shown in FIG. 2B) 62 + 65 (notshown in FIG. 2B)

The processor 42 of variable-speed drive controller 39 may be configuredto process each pair of the above two signal switch one states 62, 66and signal switch two states 63, 65 combinations and, in turn, selectfrom memory 44 and continuously furnish to the corresponding span motor38, via communications module 46, a predetermined progressivelyincreasing speed profile 75, a predetermined progressively decreasingspeed profile 77, or a new fixed current speed 76. The resultingcombinations of the present invention are as follows:

signal signal selects from memory and switch one switch two continuouslyfurnishes 66 + 65 = 75 (as shown in FIG. 10A) 62 + 63 = 77 (as shown inFIG. 10A) 66 + 63 = 76 (as shown in FIG. 10B) 62 + 65 = 76 (as shown inFIG. 10B)

FIGS. 10A and 10B illustrate the above two signal switch one states 62,66 and signal switch two states 63, 65 combinations, wherein switch one40 has either an “on” signal switch one state 66 or an “off” signalswitch one state 62 and switch two 41 has either an “on” signal switchtwo state 65 or an “off” signal switch two state 63. FIGS. 10A and 10Bfurther illustrate a predetermined progressively increasing speedprofile 75, a predetermined progressively decreasing speed profile 77,and a new fixed current speed 76 of variable-speed drive controller 39,each predetermined progressively increasing speed profile 75,predetermined progressively decreasing speed profile 77 and new fixedcurrent speed 76 based on the processing of signal switch one states 62,66 and signal switch two states 63, 65, respectively, by the processor42 of the variable-speed drive controller 39.

It is to be understood by those familiar with the art that in separateembodiments the wiring configuration of both switch one 40 and switchtwo 41 that provide the outcomes as shown in FIGS. 10A and 10B could beconfigured to provide multiple differing outcomes. FIGS. 10C and 10Dillustrate an example of differing outcomes in-lieu-of the outcomes asshown in FIGS. 10A and 10B without altering the disclosure.

With reference to FIG. 8B, the above system of the present inventiondiscussed herein provides a significant and unique improvement inoperation of irrigation systems 1 as compared to the prior art,including the prior art pertaining to all other continuous movementcontrol systems. This significant and unique improvement is the evolvingof steady state speeds of movement 78 (as shown in FIG. 8B) rather thanconstantly transitioning or transient state speeds of movement 79 (asshown in FIG. 8A) that result from span motor on 60 to span motor off 61and from span motor off 61 to span motor on 60, as required byconventional repetitive start-and-stop movement control systems of theprior art, as well as slower to faster speeds and faster to slowerspeeds, as required by all other continuous movement control systems.Furthermore, in the system of the present invention, the new fixedcurrent speeds 76 eventually evolve to steady state speeds of movement78 of the variable-speed drive assemblies 35 of each respectiveintermediate tower structure 30, 31 as the corresponding variable-speeddrive controller 39 selects from memory 44 and continuously furnishes tothe corresponding span motor 38 a predetermined progressively increasingspeed profile 75 followed by a new fixed current speed 76 and apredetermined progressively decreasing speed profile 77 followed by anew fixed current speed 76 shown in FIG. 8B. Such new fixed currentspeeds 76 eventually evolve to distinct steady state speeds of movement78 of the variable-speed drive assemblies of each respectiveintermediate tower structure 30, 31 that achieve and maintain alignmentamong a plurality of respective intermediate spans 12, 13 without theneed for constantly transitioning speeds or transient state speeds ofmovement 79 as with the repetitive start-and-stop movement controlsystems of the prior art as well all other continuous movement controlsystems.

In an example of an implementation;

-   -   1. Assume the variable-speed drive assembly 35, of the        intermediate tower structure 30 of an irrigation system 1 (FIG.        1B) having a forward movement direction 54, requires a 1.0 feet        per minute speed of movement of the variable-speed drive        assembly 35 in order to maintain intermediate span 12 in both a        non-lagging state of alignment 57 and a non-leading state of        alignment 59 with intermediate span 13 (as shown in FIG. 4A)        with steady state speeds of movement 78 (as shown in FIG. 8B).    -   2. In both a non-lagging state of alignment 57 and a non-leading        state of alignment 59 with intermediate span 13 (as shown in        FIG. 4A), a variable-speed drive controller 39 of the        variable-speed drive assembly 35 is monitoring and processing a        corresponding alignment detector 48 with a switch one 40 with an        “on” signal switch one state 66 (as shown in FIG. 2B and as        shown in upper illustration of FIG. 5A) and a switch two 41 with        an “off” signal switch two state 63 (as shown FIG. 2B and as        shown in upper illustration of FIG. 5C)    -   3. Based on the “on” signal switch one state 66 and “off” signal        switch two state 63 output of alignment detector 48, the        variable-speed drive controller 39 selects from memory 44 and        continuously furnishes to the corresponding span motor 38 a new        fixed current speed 76 (as shown in FIG. 10B) that results, in        this example, in a 1.2 feet per minute speed of movement of the        variable-speed drive assembly 35.    -   4. Subsequently, the new fixed current speed 76 (as shown in        FIG. 10B) that results, in this example, in a 1.2 feet per        minute speed of movement of the variable-speed drive assembly        35, eventually results in a leading state of alignment 58 (as        shown in right illustration of FIG. 4B) that immediately results        in switch one 40 changing from an “on” signal switch one state        66 to an “off” signal switch one state 62 (as shown in FIG. 5A),        while switch two 41 remains in an “off” signal switch two state        63 (as shown in upper illustration of FIG. 5C).    -   5. Based on the “off” signal switch one state 62 and “on” signal        switch two state 65 output of the corresponding alignment        detector 48, the variable-speed drive controller 39 selects from        memory 44 and continuously furnishes to the corresponding span        motor 38 a predetermined progressively decreasing speed profile        77 (as shown in FIG. 10A).    -   6. Subsequently, the predetermined progressively decreasing        speed profile 77 (as shown in FIG. 10A) that results in a        decreasing speed of movement of the variable-speed drive        assembly 35, eventually results in both a non-lagging state of        alignment 57 and a non-leading state of alignment 59 with        intermediate span 13 (as shown in FIG. 4A) that immediately        results in a switch one 40 changing from an “off” signal switch        one state 62 to an “on” signal switch one state 66 (as shown in        5A), while switch two 41 remains in an “off” signal switch two        state 63 (as shown in upper illustration of FIG. 5C). Such        changing from an “off” signal switch one state 62 to an “on”        signal switch one state 66 (as shown in 5A) occurring at the        exact moment the variable-speed drive assembly 35 is moving at        0.9 feet per minute.    -   7. Based on the “on” signal switch one state 66 and “off” signal        switch two state 63 output of the corresponding alignment        detector 48, the variable-speed drive controller 39 selects from        memory 44 and continuously furnishes to the corresponding span        motor 38 a new fixed current speed 76 (as shown in FIG. 10B)        that results in a 0.9 feet per minute speed of movement of the        variable-speed drive assembly 35.    -   8. Subsequently, the new fixed current speed 76 (as shown in        FIG. 10B) that results in a 0.9 feet per minute speed of        movement of the variable-speed drive assembly 35, eventually        results in a lagging state of alignment 56 (as shown in left        illustration of FIG. 4B) that immediately results in switch two        41 changing from an “off” signal switch two state 63 to an “on”        signal switch two state 65 (as shown in FIG. 5C), while switch        one 40 remains in an “on” signal switch one state 66 (as shown        in upper illustration of FIG. 5A).    -   9. Based on the “on” signal switch two state 65 and “on” signal        switch one state 66 output of the corresponding alignment        detector 48, the variable-speed drive controller 39 selects from        memory 44 and continuously furnishes to the corresponding span        motor 38 a predetermined progressively increasing speed profile        75 (as shown in FIG. 10A).    -   10. Subsequently, the predetermined progressively increasing        speed profile 75 (as shown in FIG. 10A) that results in an        increasing speed of movement of the variable-speed drive        assembly 35, eventually results in both a non-lagging state of        alignment 57 and a non-leading state of alignment 59 with        intermediate span 13 (as shown in FIG. 4A) that immediately        results in a switch two 41 changing from an “on” signal switch        two state 65 to an “off” signal switch two state 63 (as shown in        5C), while switch one 40 remains in an “on” signal switch one        state 66 (as shown in upper illustration of FIG. 5A). Such        changing from an “on” signal switch two state 65 to an “off”        signal switch two state 63 (as shown in 5C) occurring at the        exact moment the variable-speed drive assembly 35 is moving at        1.0 feet per minute.    -   11. Based on the “off” signal switch two state 63 and “on”        signal switch one state 66 output of the corresponding alignment        detector 48, the variable-speed drive controller 39 selects from        memory 44 and continuously furnishes to the corresponding span        motor 38 a new fixed current speed 76 (as shown in FIG. 10B)        that results in a 1.0 feet per minute speed of movement of the        variable-speed drive assembly 35.    -   12. Subsequently, the evolved new fixed current speed 76 (as        shown in FIG. 10B) that results in a 1.0 feet per minute speed        of movement of the variable-speed drive assembly 35 maintains        intermediate span 12 in both a non-lagging state of alignment 57        and a non-leading state of alignment 59 with intermediate span        13 (as shown in FIG. 4A) with steady state speeds of movement 78        (as shown in FIG. 8B).

In an implementation, one or more intermediate tower structures 30, 31may be controlled by a suitable variable-speed drive assembly 35, or thelike, to assist in traversing the irrigation system 1 over a respectiveground surface, cultivation area or field. For example, eachintermediate tower structure 30, 31 may include a variable-speed driveassembly 35 to propel the respective intermediate tower structure 30, 31over a respective ground surface, cultivation area or field in either aforward movement direction 54 or a reverse movement direction 55. Itshould be noted that the system of the present invention does notrequire a variable-speed drive assembly 35 at the end tower structure 32(i.e., end tower structure 32 does not require a variable-speed driveassembly 35 that includes an alignment detector 48; and, therefore, endtower structure 32 does not require either a switch one 40 or a switchtwo 41). End tower structure 32 can be controlled using a fixed-speeddrive controller 37, a variable-speed drive controller 39, or by othermeans known in the art.

As described above and with reference to FIG. 2B, the variable-speeddrive assembly 35 may incorporate one or more span motors 38 configuredto drive the irrigation system 1 in a forward movement direction 54 or areverse movement direction 55 based on the configuration of 3-phasesupply power 67 conductor-L1 68, conductor-L2 69 and conductor-L3 70. Ineither a forward movement direction 54 or a reverse movement direction55, the substantial straight alignment between each intermediate span12, 13 and between the outermost intermediate span 13 and the end span14 of the irrigation system 1 is maintained by the rotation of one ormore cams 83, rotated by one or more rods 87, such cams 83 rotatingagainst roller-actuating arm one 88 of a corresponding switch one 40 androller-actuating arm two 89 of a corresponding switch two 41 ofalignment detector 48 at each intermediate span 12, 13 flexible juncture(not shown) on intermediate tower structures 30, 31.

With reference to FIGS. 2B, 5A and 6A, assuming a forward movementdirection 54, the switch one 40 is configured to signal either an “on”signal switch one state 66 (e.g., energized via normally closed switchone contact 80 closed to common switch one contact 82 to allow a forwarddirection signal 22 from incoming span cable 20 to pass through switchone 40 to variable-speed drive controller 39 as shown in upperillustration of FIG. 5A) or an “off” signal switch one state 62 (e.g.,not energized via normally closed switch one contact 80 opened to commonswitch one contact 82 to prevent a forward direction signal 22 fromincoming span cable 20 to pass through switch one 40 to variable-speeddrive controller 39 as shown in lower illustration of FIG. 5A).

Again, with reference to FIGS. 2B, 5B and 6A, assuming a reversemovement direction 55, the switch one 40 is configured to signal eitheran “on” signal switch one state 66 (e.g., energized via normally openedswitch one contact 81 closed to common switch one contact 82 to allow areverse direction signal 23 from incoming span cable 20 to pass throughswitch one 40 to variable-speed drive controller 39 as shown in lowerillustration of FIG. 5B) or an “off” signal switch one state 62 (e.g.,not energized via normally opened switch one contact 81 opened to commonswitch one contact 82 to prevent a reverse direction signal 23 fromincoming span cable 20 to pass through the switch one 40 tovariable-speed drive controller 39 as shown in upper illustration of5B).

With reference to FIGS. 2B, 5C and 6B, assuming a forward movementdirection 54, the switch two 41 is configured to signal either an “off”signal switch two state 63 (e.g., not energized via normally openedswitch two contact 85 opened to common switch two contact 86 to preventa forward direction signal 22 from incoming span cable 20 to passthrough switch two 41 to variable-speed drive controller 39 as shown inupper illustration of 5C) or an “on” signal switch two state 65 (e.g.,energized via normally opened switch two contact 85 closed to commonswitch two contact 86 to allow a forward direction signal 22 fromincoming span cable 20 to pass through switch two 41 to variable-speeddrive controller 39 as shown in lower illustration of 5C).

Again, with reference to FIGS. 2B, 5D and 6B, assuming a reversemovement direction 55, the switch two 41 is configured to signal eitheran “on” signal switch two state 65 (e.g., energized via normally closedswitch two contact 84 closed to common switch two contact 86 to allow areverse direction signal 23 from incoming span cable 20 to pass throughswitch two 41 to variable-speed drive controller 39 as shown in upperillustration of 5D) or an “off” signal switch two state 63 (e.g., notenergized via normally closed switch two contact 84 opened to commonswitch two contact 86 to prevent a reverse direction signal 23 fromincoming span cable 20 to pass through switch two 41 to variable-speeddrive controller 39 as shown in lower illustration of 5D).

With reference to FIGS. 2B, 4A, 4B and 5A in an embodiment with aforward direction signal 22, an “on” signal switch one state 66 (asshown in upper illustration of FIG. 5A) may be defined as anyintermediate span 12, 13 being in a non-leading state of alignment 59(as shown in FIGS. 4A and 4B) with one or more adjacent intermediatespans 12, 13 or end span 14 along a generally linear longitudinal axis(e.g., defined with respect to a generally horizontal surface, such asthe ground). Similarly, with a forward direction signal 22, an “off”signal switch one state 62 (as shown in lower illustration of FIG. 5A)may be defined as any intermediate span 12, 13 being in a leading stateof alignment 58 (as shown in FIG. 4B) with one or more adjacentintermediate spans 12, 13 or an end span 14 along a generally linearlongitudinal axis (e.g., defined with respect to a generally horizontalsurface, such as the ground).

With reference to FIGS. 2B, 4A, 4B and 5C in an embodiment with aforward direction signal 22, an “off” signal switch two state 63 (asshown in upper illustration of FIG. 5C) may be defined as anyintermediate span 12, 13 being in a non-lagging state of alignment 57(as shown in FIGS. 4A and 4B) with one or more adjacent intermediatespans 12, 13 or end span 14 along a generally linear longitudinal axis(e.g., defined with respect to a generally horizontal surface, such asthe ground). Similarly, with a forward direction signal 22, an “on”signal switch two state 65 (as shown in lower illustration of FIG. 5C)may be defined as any intermediate span 12, 13 being in a lagging stateof alignment 56 (as shown in FIG. 4B) with one or more adjacentintermediate spans 12, 13 or an end span 14 along a generally linearlongitudinal axis (e.g., defined with respect to a generally horizontalsurface, such as the ground).

With reference to FIGS. 2B, 4A, 4C and 5B in an embodiment with areverse direction signal 23, an “off” signal switch one state 62 (asshown in upper illustration of FIG. 5B) may be defined as anyintermediate span 12, 13 being in a non-leading state of alignment 59(as shown in FIGS. 4A and 4C) with one or more adjacent intermediatespans 12, 13 or end span 14 along a generally linear longitudinal axis(e.g., defined with respect to a generally horizontal surface, such asthe ground). Similarly, with a reverse direction signal 23, an “on”signal switch one state 66 (as shown in lower illustration of FIG. 5B)may be defined as any intermediate span 12, 13 being in a leading stateof alignment 58 (as shown in FIG. 4C) with one or more adjacentintermediate spans 12, 13 or an end span 14 along a generally linearlongitudinal axis (e.g., defined with respect to a generally horizontalsurface, such as the ground).

With reference to FIGS. 2B, 4A, 4C and 5D in an embodiment with areverse direction signal 23, an “on” signal switch two state 65 (asshown in upper illustration of FIG. 5D) may be defined as anyintermediate span 12, 13 being in a non-lagging state of alignment 57(as shown in FIGS. 4A and 4C) with one or more adjacent intermediatespans 12, 13 or end span 14 along a generally linear longitudinal axis(e.g., defined with respect to a generally horizontal surface, such asthe ground). Similarly, with a reverse direction signal 23, an “off”signal switch two state 63 (as shown in lower illustration of FIG. 5D)may be defined as any intermediate span 12, 13 being in a leading stateof alignment 58 (as shown in FIG. 4C) with one or more adjacentintermediate spans 12, 13 or an end span 14 along a generally linearlongitudinal axis (e.g., defined with respect to a generally horizontalsurface, such as the ground).

It is to be understood that in a separate embodiment the signal switchone states 62, 66 and signal switch two states 63, 65 could beconfigured in an opposite manner to the above discussion (notillustrated) for both a forward direction signal 22 and a reversedirection signal 23 without altering the disclosure.

More generally, it is to be understood that both the switch one 40 andswitch two 41, of alignment detector 48, each essentially functions as aswitch having two signal switch states (e.g., an “on” signal switch onestate 66 and an “off” signal switch one state 62 and an “on” signalswitch two state 65 and an “off” signal switch two state 63) to signalfour distinct states of alignment of adjacent spans along a generallylinear longitudinal axis. For example, the switch one 40 most commonlyfound on conventional center pivot irrigation systems may signal an“off” signal switch one state 62 when the intermediate spans 12, 13 arein a leading state of alignment 58, and may signal an “on” signal switchone state 66 when the intermediate spans 12, 13 are in a non-leadingstate of alignment 59. This could be reversed, so that the switch one 40may signal an “on” signal switch one state 66 when the intermediatespans 12, 13 are in a lagging state of alignment 56, and may signal an“off” signal switch one state 62 when the intermediate spans 12, 13 arein a non-lagging state of alignment 57. Further, the switch two 41 ofthe present invention may signal an “off” signal switch two state 63when the intermediate spans 12, 13 are in a non-lagging state ofalignment 57, and may signal an “on” signal switch two state 65 when theintermediate spans 12, 13 are in a lagging state of alignment 56. Thiscould be reversed, so that the switch two 41 may signal an “on” signalswitch two state 65 when the intermediate spans 12, 13 are in anon-leading state of alignment 59, and may signal an “off” signal switchtwo state 63 when the intermediate spans 12, 13 are in a non-leadingstate of alignment 59. It is entirely a matter of design choice as towhich switch one 40 and switch two 41 states correspond to an on or anoff, a high or a low, a positive or a negative, etc., signal switch one40 and switch two 41 states, respectively. In addition, it should benoted that the terms “leading”, “lagging”, “non-leading”, and“non-lagging” are relative to the direction of rotation or movementdirection 54, 55 of the intermediate spans 12, 13 at any particulartime, since most conventional irrigation systems can be operated ineither direction of movement 54, 55 under the control of the operator.

It is to be understood that in the system of the present invention the“on” signal switch one state 66 and “off” signal switch one state 62 maybe signaled from one or more switches one 40, of alignment detector 48,each having two or more switch one 40 states and the “on” signal switchtwo state 65 and “off” signal switch two state 63 may be signaled fromone or more switches two 41, of alignment detector 48, each having twoor more switch two 41 states. Furthermore, it is to be understood thatin the system of the present invention, the alignment detector 48 mayinclude a single switch, configured to signal three or more signalswitch states in-lieu-of both switch one 40 and switch two 41 of thealignment detector 48 disclosed herein. The present invention could alsobe implemented using any type of alignment detector 48, that comprises aswitch one 40 and a switch two 41, a plurality of switches one 40 andswitches two 41, an analog sensor 47 (e.g., a potentiometer) or aplurality of analog sensors 47, to detect and output the state ofalignment of the intermediate spans 12, 13 and end span 14.

In an embodiment of the present invention, the variable-speed drivecontroller 39 monitors and processes the signal switch one states 62, 66and signal switch two states 63, 65 of the corresponding alignmentdetector 48 and, based on combinations of such signal switch one states62, 66 and signal switch two states 63, 65, selects from memory 44 andcontinuously furnishes to the corresponding span motor 38 apredetermined progressively increasing speed profile 75, a predeterminedprogressively decreasing speed profile 77, or a new fixed current speed76.

In particular, as shown in FIGS. 10A, 10B, 10C and 10D, thevariable-speed drive controller 39 selects from memory 44 andcontinuously furnishes to the corresponding span motor 38 apredetermined progressively increasing speed profile 75, a predeterminedprogressively decreasing speed profile 77, or a new fixed current speed76 so as to maintain substantial straight alignment of the respectivelongitudinal axes of the intermediate spans 12, 13 and end span 14 aspreviously discussed.

In a preferred embodiment and as shown in FIG. 3C, the variable-speeddrive controller 39 may include a processor 42 configured to provideprocessing for signal switch one states 62, 66 and signal switch twostates 63, 65 data and, in turn, select from memory 44 and continuouslyfurnish to the corresponding span motor 38 a predetermined progressivelyincreasing speed profile 75, a predetermined progressively decreasingspeed profile 77, or a new fixed current speed 76.

Thus, the processor 42 may execute one or more control logic programsand/or instructions described herein. The variable-speed drivecontroller 39 may also include a memory 44, which is an example oftangible computer-readable media that provides storage functionality tostore various data associated with the operation of the variable-speeddrive controller 39, such as software programs/modules and code segmentsmentioned herein, or other data to instruct the processor 42 to performthe steps described herein. Finally, the variable-speed drive controller39 may include a communications module 46, which is configured tocommunicate with other components of variable-speed drive assembly 35(e.g., span motors 38, switch one 40, switch two 41 (as in FIG. 2B))over a communication network (e.g., a wireless network, a wired network,etc.). For example, the communications module 46 of variable-speed drivecontroller 39 may be directly coupled (e.g., connected via one or morewires, or the like) to a corresponding switch one 40 and switch two 41of alignment detector 48 and to the corresponding span motor 38 ofvariable-speed drive assembly 35. The communications module 46 may berepresentative of a variety of communication components andfunctionality, including, but not limited to, one or more antennas, atransmitter and/or receiver, a transceiver, or the like.

As described above and with reference to FIG. 1B, the irrigation system1 may include one or more variable-speed drive assemblies 35 at anintermediate tower structure 30, 31. Each variable-speed drive assembly35 may include one or more span motors 38. A non-limiting list ofsuitable span motor 38 types includes a magnetic electric motor, anelectrostatic electric motor, a piezoelectric electric motor, aself-commutated DC (direct current) motor, a DC SRM (switched reluctancemotor), a DC variable reluctance motor, a stepper motor, an AC(alternating current) asynchronous induction motor, or an AC synchronousreluctance motor, and the like.

As shown in FIGS. 2B and 3B, each variable-speed drive assembly 35 mayinclude a variable-speed drive controller 39. A non-limiting list ofsuitable variable-speed drive controller 39 types includes an AC(alternating current) VFD (variable frequency drive), a variable-torqueV/Hz (volts-per-hertz) control VFD, a flux control VFD, a DTC (directtorque control) VFD, a sensorless vector control VFD, a sensored vectorcontrol VFD, a brush type DC (direct current) variable-drive controlunit, or a DC variable-drive control unit, and the like, all with orwithout an internal or an external microcontroller or an internal or anexternal PLC (programmable logic controller).

While FIG. 2B illustrates that the variable-speed drive controller 39 isincorporated inside (e.g., housed within) the variable-speed driveassembly 35, it is to be understood that the variable-speed drivecontroller 39 may be a standalone unit. Furthermore, the elements ofprocessor 42, memory 44 and communications module 46 of variable-speeddrive controller 39 could each be standalone and not configured to beincorporated inside (e.g., housed within) the variable-speed drivecontroller 39 as shown in FIG. 3C.

As shown in FIG. 3B, the variable-speed drive controller 39 is directlyconnected with the respective switch one 40 and switch two 41 (e.g., viaa wired connection) of alignment detector 48. A non-limiting list ofsuitable switch one 40 and switch two 41 types includes a single-pole,double-throw (SPDT) switch (as illustrated by switch one 40 in FIGS. 2A,2B, 5A and 5B and as illustrated by switch two 41 in FIGS. 2B, 5C and5D), a micro switch, a limit switch, a biased switch, a rotary switch, atoggle switch, a magnetic switch, a reed switch, a mercury switch, acompass switch, a photo infrared switch, a motion switch, a Hall-effectswitch, a capacitance switch, an induction switch, a digital encoderswitch, a position resolver switch, a guided wire switch, a GPS (globalpositioning system) based alignment switch, a laser based alignmentswitch, a non-contact proximity switch, and the like. In thisimplementation, the variable-speed drive controller 39 is also directlyconnected to the respective span motor 38 (e.g., via a wiredconnection).

As shown in FIGS. 3E and 3F, the variable-speed drive controller 39 isdirectly connected with the respective analog sensor 47 (e.g., via awired connection) of the alignment detector 48. A non-limiting list ofsuitable analog sensor 47 types includes a potentiometer, a captivealignment sensor, a laser based alignment sensor, a non-contactproximity sensors, or any other device capable of signaling at leastthree distinct states of alignment, and the like. In thisimplementation, the variable-speed drive controller 39 is also directlyconnected to the respective span motor 38 (e.g., via a wiredconnection).

In an embodiment and as shown in FIGS. 2B and 3B, switch one 40 andswitch two 41, of alignment detector 48, are each in communication witha respective variable-speed drive controller 39. Conventionally and withreference to FIGS. 5A, 5B, 5C and 5D, switch one 40 and switch two 41each may be actuated, but in opposite manners, respectively, by themovement of a cam 83 (shown in FIG. 2B) on a shaft connected to acorresponding rod 87 associated with a corresponding intermediate span12, 13.

Conventionally, selection of either a forward movement direction 54 or areverse movement direction 55 by operators of irrigation system 1 usinga central control panel (not shown) at center pivot point structure 2 ora remote control system (not shown) at one or more intermediate towerstructures 30, 31 or end tower structure 32 determines whether theforward direction signal 22 or the reverse direction signal 23 (shown inFIGS. 2B, 5A, 5B, 5C and 5D) is present (i.e., carrying either a forwarddirection signal 22 or a reverse direction signal 23 through both switchone 40 using normally closed switch contact 80, normally opened switchcontact 81, and common switch contact 82 and switch two 41 usingnormally closed switch contact 84, normally opened switch contact 85,and common switch contact 86), such switch one 40 and switch two 41 maybe conventional (e.g., single-pole, double-throw (SPDT) switch alsosometimes referred to as a limit switch or a micro switch).

In an embodiment of the present invention and with reference to FIGS.2A, 4A, 4B and 4C, the conventional alignment detector 48, that mayinclude a switch one 40 with a roller-actuating arm one 88 and thecorresponding actuating rod 87 and cam 83, is already included andconfigured in the installed base of existing electric powered irrigationsystems 1. As such, the basic elements of the alignment systems of theprior art can be readily used by the system of the present invention toindicate a lagging state of alignment 56, a non-lagging state ofalignment 57, a leading state of alignment 58, or a non-leading state ofalignment 59 between the corresponding intermediate spans 12, 13 and theend span 14 for a movement direction 54, 55.

In one or more implementations and with reference to FIGS. 4A, 4B, 4C,5A and 5B, each switch one 40 when actuated or not actuated may beconfigured to indicate when a respective intermediate span 12, 13 is ina lagging state of alignment 56, a non-lagging state of alignment 57, aleading state of alignment 58, or a non-leading state of alignment 59.

In one or more implementations and with reference to FIGS. 4A, 4B, 4C,5C and 5D, each switch two 41 when actuated or not actuated may beconfigured to indicate when a respective intermediate span 12, 13 is ina lagging state of alignment 56, a non-lagging state of alignment 57, aleading state of alignment 58, or a non-leading state of alignment 59.

Although the subject matter has been described in language specific tostructural features and/or process operations, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

We claim:
 1. An irrigation system having a movement direction over aground surface of a field, the irrigation system comprising: a pluralityof spans, each having a longitudinal axis, said plurality of spans beingconnected at a flexible juncture and having a state of alignment of therespective longitudinal axes of the plurality of spans; an intermediatetower structure between the plurality of spans configured to support theplurality of spans above the ground surface; a variable-speed driveassembly of the intermediate tower structure having a wheel configuredto contact the ground surface below the irrigation system and a spanmotor configured to drive the wheel so as to propel the intermediatetower structure over the ground surface; an alignment detector to detectand output the state of alignment of the respective longitudinal axes ofthe plurality of spans indicating: (a) a lagging state of misalignment;(b) a leading state of misalignment; or (c) a state of alignment that isneither lagging nor leading; and a variable-speed drive controller ofthe variable-speed drive assembly controlling the speed of theintermediate tower structure over the ground surface, saidvariable-speed drive controller monitoring and processing the output ofthe alignment detector and, based on the state of alignment detected bythe alignment detector: (a) progressively increasing the speed of thespan motor over time while in the lagging state of misalignment; (b)progressively decreasing the speed of the span motor over time while inthe leading state of misalignment; or (c) maintaining the current speedof the span motor while in the state of alignment that is neitherlagging nor leading, to thereby maintain substantial straight alignmentof the respective longitudinal axes of the plurality of spans.
 2. Thesystem for claim 1 wherein the alignment detector comprises an analogsensor.
 3. The system of claim 1 wherein the alignment detectorcomprises a potentiometer.
 4. The system of claim 1 wherein thealignment detector comprises a plurality of switches.
 5. The system ofclaim 1 wherein the alignment detector comprises a capacitivedisplacement sensor.
 6. The system of claim 1 wherein the alignmentdetector comprises a strain gauge sensor.
 7. The system of claim 1wherein the alignment detector comprises a non-contact proximity sensor.8. The system of claim 1 wherein the alignment detector comprises acaptive alignment sensor.
 9. The system of claim 1 wherein the alignmentdetector comprises a laser-based alignment sensor.